Sampling method



CRSSS REFERENCE SEARCH '00M July 22, 1969 c. c. BOMBARDIERI sAMPLING METHOD Filed Nov. 7. 1966 FIG.

ted States Patent O i.;

Patented July 22, i969 3,456,504 SAMPLING METHOD Caurino C.. Bombardieri, Calgary, Alberta, Canada, assignor to Esso Production Research Company, a corporation of Delaware Filed Nov. 7, 1966, Ser. No. 592,398 j ",Int. Cl. E21b 47/00 U.S. Cl. 73--151 5 Claims ABSTRACT OF THE DISCLOSURE A method for analyzing a subsurface formation which involves the introduction of at least two iiuids into said formation in ia, selected ratio, a further production of fluids from said formation and an analysis of the return fluids for relative amounts of said two injected fluids.

y termined ratio arid then sampling and analyzing the treating fluids returned from the formation to determine the ratio of these uids and thereby the nature of the formation fluids.

In one preferred mode of operation, method and appan ratus are described for detecting hydrocarbons in porous rock in which a predetermined ratio of two specific gases, one of which has preferentially high solubility in hydrocarbons compared with its solubility in formation water, and the other of which has low solubility in both hydrocarbons and formation water, is injected under pressure into a porous formation. The gas returned to the borehole is sampled and analyzed, as, for example, by well-known gas chromatography techniques which require only a small amount of returned fluids for an accurate detera mination of identity and amount thereof. A significant ratio change of the injected gases is an indication of the presence of hydrocarbons, whereas a negligible ratio change is an indication of the absence of hydrocarbons.

Thus, this invention makes use of the high and prefer ential solubility property of specific gases, e.g., carbon dioxide in hydrocarbons, and the relatively low solubility property of these, gases in brine and the relative insolu= bility of other gases, e.g., nitrogen, in both hydrocarbons and brine. A predetermined ratio of nitrogen to carbon dioxide gas is introduced under pressure into a forma= tion to be treated and a sample of the returned gas is analyzed for both nitrogen and carbon dioxide. Any loss of nitrogen is considered to have dissipated into the formation and it is considered that an equivalent amount of carbon dioxide gas has also been lost by dissipation. Any further and significant changes in the amount of carbon dioxide would be due to solubility of carbon dioxide in hydrocarbons.

The gases to be injected into the formation are placed under pressure in one chamber of a tool which is adapted to provide an isolated iiow path for these gases into the formation to be treated. Another chamber in this tool receives a sample of gas returned from the formation through an isolated ilow path. A tool for carrying out this technique may be suitably shoot and test apparatus such as disclosed and claimed in U.S. Patent No. 3,153,449, entitled Method and Apparatus for Complet-1 ing a Well, issued Oct. 20, 1964 to M. P. Lebourg,

modified to provide chambers for the injected and returned gases -a-nd suitable valving in place of the fluid treating chambers and valves shown in this patent.

Aprimary object of the present invention is to provide new landimproved method and apparatus .for determining characteristics of subsurface iiuids and especially the presencer o f hydrocarbons in subsurface formations.

Briefly, the method of this invention comprises intro-1 ducing, atleast two iiuids into a subsurface formation in a selected ratio; producing fluids from said formation; and analyzing said returned fluids for relative amounts of said two injected fluids.

The apparatus of this invention briefly comprises a tool having an elastomer, annular-shaped sealing member for isolating an area along the length of the bore from well bore fluid contained in the well bore; means in the tool for engaging the wall of the Well bore to promote contact of the sealing member with the well bore and isolation of said area; said tool having a first chamber adapted to contain initially fluid to be .injected into a subsurface formation and a second chamber adapted to receive well fluids from said formation; perforator means suitably aligned with a central portion fof said sealing member and arranged to develop a perforation in the earth formations in fluid communication with said isolated area; said tool including passageway means adapted to provide isolated flow paths from said first chamber to said isolated area and from said isolated area to said second chamber; valve means arranged in said passageway means adapted to permit and prevent iiow of fluids from and to, respectively, said first chamber and to permit and prevent ow of fluids to and froms respectively, said second chamber.

The above object and other objects and advantages of the invention will be apparent from a more detailed description thereof when taken with the drawings wherein:

FIGS. 1 and 1A are views showing the well tool of the invention, partly in section, and in position in a borehole for carrying out the method of this invention; and

FIG. 2 is a detailed view of a suitable valve arrange= ment usable in the apparatus illustrated in FIG. 1.

As shown in FIG. 1, borehole 10, in which is arranged a well or casing pipe 12 cemented in place by cement sheath 13, traverses a subsurface 'formation 11. A shoot and test tool 15 is suspended in casing pipe 12 by means of a conductor` cable 16. Tool 15 includes a tubular body member 17 provided with reservoirs or chambers 18 and 19 separated byy a barrier 20. Chamber 18 initially con= tains gases undelr; pressure higher than the formation pres=l sure. Chamber receives well fluids from fthe formation following injection of the gases initially contained in chamber 18 into formation 11. Chamber 19 is previously purged of gases and is at a reduced pressure less than formation pressure to permit return ilow of well uids, in= cluding liquids and gases initially contained in the formas1 tion as well as injected gases, following injection of gases initially contained in chamber 18. A conduit or passage way 21 uidly communicates chamber 18 and the upper portion of a conduit or passageway 22, which passageway extends between chamber 19 and a chamber 23 in the gun block 24 of tool 15. Valves 25 and 26 are arranged in passageways 21 and 22, respectively. These valves may be suitably solenoid-operated valves such as illustrated in FIG. 2. As seen in this figure, a valve member 27 is nor= mally biased by spring 28 to avvalve seat 29 vrformed in passageway 21 (and 22). Actuaton of the solenoid 30 causes plunger 31 to dectract and remove valve 27 from seat 29 again the bias of spring 28 and open the passages way(s). An annular sealing pad 34 surrounds chamber 23 in which is located a jet perforator gun 35; a backoff shoe 36 is positioned on the opposite side of tool 15 from the location of pad 34. Backotf shoe 36 has connected to it piston rods 37, which in turn are connected to pistons which are received in lhydraulic cylinders within the tool as shown. Tension springs 38 facilitate retraction of backoif shoe 3S from the wall of pipe 12. A hydraulic actuating system for piston rods 36 may be of the type illustrated in U.S. Patent No. 2,674,313, issued to Chambers. In operating in accordance with the present invention, tool 1S is lowered to adacent formation 11. A section of pipe 12 encircled by pad 34 is isolated from uids within pipe 12 by actuating pistons connected to piston rods 37 to Iforce backoif shoe 36 against the wall of pipe-12 against the bias of springs 38. Formation 11 is then penetrated by actuating jet chrge 3S to form a perforation 40 in formation 11. Chamber 23 may be permitted to receive any .mud which might be entrapped within the isolated section from the formations by momentary production of the perforation. Valve 25 is then opened and gases contained in chamber 18 flow through passageway 21 and portion of passageway 22 into chamber 23 and into formation r11 through isolated perforation 40. Valve 25 is then closed and valve 26 is opened to permit well uids mixed with the injected gases to ow from perforation 40 and through passageway 22 into chamber 19 which is at a lower presa sure than the formation pressure. Then, valve 26 is closed. The seal provided by pad 34 is removed by retracting shoe 36 and tool 15 is removed from casing 12 by cable 16. At the surface, chamber 19 is opened and the fluids contained therein are analyzed.

Assuming that the gas system to be used is carbon dia oxide and nitrogen, predetermined ratios of nitrogen to carbon dioxide could vary from 0.l:l.0 to l0.0:1.0 with an optimum amount determined by selective testing. The solubility properties of carbon dioxide and nitrogen gas are discussed in The Use of Nitrogen and Carbon Dioxide to Improve Well Stimulation Treatments, Spring Meeting of the Rocky Mountain District, American Petroleum Institute, Paper No. 875-17-B, Apr. 24-26, 1963, by I. P. Moran. Other papers relating to the solubility of cara bon dioxide in hydrocarbons are Phase Relations of Carbon Dioxide-Hydrocarbon Mixture, Producers Monthly, Dec. 19, 1964, vol. 17, by C. Drew, and Generalized Correlations for Predicting Solubility, Swelling and Viseosity Behavior of CO2-Crude Oil Systems, Journal of Petroleum Technology, January 1965, vol. 102, by R. Simon and D. I. Graue.

The following example calculations were made based on solubility data set forth in the above-mentioned papers:

Assuming an initial 1:1 ratio of nitrogen and carbon dioxide at a pressure of 1,000 p.s.i., the rao of the gases upon return for a water-oil ratio of :1 in the formation would be 20.721 nitrogen to carbon dioxide; a water-oil ratio of 1:1 in the `formation would give a ratio of the gases upon return of nitrogen to carbon dioxide of 34.7: l, and a ratio of water to oil in the formation of 1:10 would give a ratio of gases upon return of nitrogen to carbon di= oxide of 40.731.

Other gas systems in accordance with the principle of the present invention might be used instead of the ntro= gen-carbon dioxide gas system. Typical examples of these other gases which have low solubility in water and some or greater solubilities in oil are acetylene, ethylene, oxygen and carbon monoxide. These and other gases having desirable solubility properties which can be used will be recognized by those skilled in the art.

Although the invention described herein is a method to be used for detecting hydrocarbons, it can also be used to detect other formation uids, such as brine. In this .instance, a gas which has high solubility in brine and low solubility in hydrocarbons could be used as the test fluid. Analysis of the return fluids can also be used to identify the presence of other gases or fluids in the rock formation in addition to the gases injected from the tool. I

Various modifications in the invention may be made without departing from the spirit and scope thereof.

Having fully described the apparatus, method and operation of my invention, I claim:

1. A method for determining characteristics of subsurface formation uids comprising:

introducing at least two uids into a subsurface formation in a selected ratio, each of said fluids having different solubilities in said formation fluids;

producing fluids Ifrom said formation; and

analyzing said uids produced from said formation and determining the ratio of said introduced uids in said produced fluids.

2. A method as recited in claim' 1 in which one of said introduced uids has preferentially higher solubility in hydrocarbons fand relatively low solubility in formation water and another of said introduced fluids has relatively low solubility in both hydrocarbons and formation water whereby a ratio change of said introduced fluids indicates the presence of hydrocarbons and no ratio change of said introduced iiuids indicates absence of hydrocarbons.

3. A method as recited in claim 2 in which said one uid is carbon dioxide and said other uid is nitrogen.

4. A method as recited in claim 3 in which said selected ratio of nitrogen to carbon dioxide ranges from 0.1:1.0 to 10.0:1.0.

5. A method as recited in claim 1 in which one of said introduced fluids has preferentially higher solubility in formation water and relatively low solubility in hydrocarbons and another of said introduced fluids has relatively low solubility in both formation water and hydrocarbons whereby a ratio change of the introduced uids indicates the presence of water and no ratio change of said introduced fluid indicates absence of water.

References Cited UNITED STATES PATENTS 3,010,023 11,/ 1961 Egan et al.

3,254,531 6/1966 Briggs 166-3 X 3,289,474 12/1966 Smith 73-155 3,008,521 l1/1961 Boucher 73--151 RICHARD C. QUE'ISSER, Primary Examiner J. W. MYRACLE, Assistant Examiner US, Cl. XR. 

